Corona-Imaging Colorimetric Method for Accurate Measurement of the Size of Water Droplets in an Expansion Chamber

Abstract

Accurate and time-resolved measurement of the size of water droplets is a prerequisite for the study of the microphysical processes of cloud formation by using an expansion chamber. We developed a droplet sizing method that uses color images of coronae observed under illumination of a white-light beam, also known as the corona-imaging colorimetry (CIC) method. In the CIC method, RGB data from images obtained by a commercial digital camera are converted into standard colorimetric parameters. The droplet size is estimated by optimizing the agreement of the measured colorimetric parameters with those estimated from Mie theory. For polystyrene latex spheres suspended in water, the particles size estimated by the CIC method agrees to within 2% of the predetermined value. We apply this method to the time-resolved measurement of the size of water droplets formed in an expansion chamber. The CIC method is technically simple and enables accurate and instantaneous measurements of the size of droplets with diameters larger than about 10 μm, which is the typical size of cloud droplets that form in the atmosphere.

Copyright 2013 American Association for Aerosol Research

Acknowledgments

This work was supported by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), the Strategic International Cooperative Program of the Japan Science and Technology Agency (JST), the Global Environment Research Fund of the Japanese Ministry of the Environment (A-0803 and A-1101), and the GRENE Arctic Climate Change Research Project. The authors would like to thank S. Ohata for his support of the laboratory experiments.